1. Field of the Invention
This invention primarily relates to a method of making primary alcohol-acid esters from dicarboxylic acid monoesters and polymerizing the primary alcohol-acid esters to form new polymers. More particularly, it relates to the selective reduction of dicarboxylic acid monoesters with diborane to produce monomers of extremely high purity.
2. Description of the Prior Art
Primary alcohol-acid esters, such as methyl p-hydroxymethylbenzoate (Me pHMB), methyl m-hydroxymethylbenzoate (Me mHMB), and methyl 6-hydroxymethyl-2naphthoate are known in the art. Of particular interest has been methyl p-hydroxymethylbenzoate and its corresponding acid, p-hydroxymethylbenzoic acid (pHMBA), which has been synthesized for use as a monomer to make the corresponding homopolymer, poly (p-methylenebenzoate). The acid is believed to have been prepared first as early as 1872 by free-radical bromination of p-toluic acid to p-bromomethyltoluic acid, hydrolysis with aqueous barium hydroxide, and subsequent purification by recrystallization from water. Other methods for the preparation of Me pHMB or pHMBA have been discovered since, including:
(a) Hydrolysis of p-toluic acid and derivatives functionalized at the benzylic position, such as p-halomethylbenzoic acid and esters, p-halomethylbenzonitrile, p-hydroxymethylbenzonitrile; and p-chloromethylbenzoyl chloride. PA1 (b) Oxidation of p-xylene and substituted p-xylenes, such as p-hydroxymethyltoluene, p-acetoxymethyltoluene, and p-xylenediol, and oxidation of p-toluic acid, p-tolualdehyde, and derivatives. PA1 (c) Chloromethylation of benzoic acid and toluene derivatives. PA1 (d) Carboxylation of p-halotoluene compounds via lithium salts. PA1 (e) Disproportionation of terephthaldehyde (Cannizzaro reaction). PA1 (f) Polarographic reduction of dimethyl terephthalate.
A low molecular weight poly (p-methylenebenzoate) has been previously prepared from p-hydroxymethylbenzoic acid and its corresponding methyl and ethyl esters. The polymers thus produced however have been very brittle and are characterized by an inherent viscosity of less than about 0.40 dl/g. (deciliters per gram). As such these polymers are relatively useless. Prior to this invention it has not been known whether the inability to achieve a higher molecular weight (and hence a higher inherent viscosity) has been due to monomer impurity, polyesterification conditions, some intrinsic properties of the monomers to undergo side reactions that limit the degree of polymerization such as ether formation, oxidation, or decomposition, or to some combination of two or more of these factors. Recent work by others confirms that the problem has not been solved. (See Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 1, p. 83 (1976)).
Accordingly, it is an object of this invention to develop a method for making a useful higher molecular weight poly (p-methylenebenzoate) having good impact resistance and characterized by an inherent viscosity greater than about 0.60 dl./g.
It is also an object of this invention to develop a method for producing high purity primary alcohol-acid esters from dicarboxylic acid monoesters.
It is a specific object of this invention to develop a method for producing high purity methyl p-hydroxymethylbenzoate, methyl m-hydroxymethlylbenzoate, and methyl 6-hydroxymethyl-2-naphthoate and polymers therefrom.
These and other objects will become apparent upon further reading of the specification.